The invention relates to a method of making, filling, and closing re-entrant receptacles having rims of diameter smaller than the diameter of the bodies of said receptacles, in which method a strip of thermoplastic material is caused to advance stepwise, and between two successive advances of said strip, a transverse row of receptacles is made by thermoforming said strip, a row of receptacles made in a preceding cycle is filled, the filled receptacles of another row are closed with a covering, and the receptacles that were closed in an earlier cycle are separated from the strip of thermoplastic material.
The invention also relates to an installation for making, filling, and closing re-entrant receptacles presenting rims of diameter smaller than the diameter of the bodies of said receptacles, the installation comprising means for causing a strip of thermoplastic material to advance stepwise, and comprising from upstream to downstream in the stepwise advance direction of said strip: a thermoforming station suitable for thermoforming a transverse row of receptacles in said strip; a filling station for filling a row of receptacles; a closing station for closing a row of filled receptacles with a covering; and a separator station for separating a row of closed receptacles from the strip of thermo-plastic material.
When thermoforming receptacles that are not re-entrant in a strip of thermoplastic material, a covering strip is applied to the filled receptacles, the strip is sealed onto the rims of the receptacles, and the covering strip and the strip of thermo-plastic material are cut together in a separator station having an upper cutting tool and a lower backing tool, the tool and the backing tool being movable vertically to move towards each other during a processing cycle to separate filled receptacles that have been closed by means of a covering. When the receptacles are for presenting in groups of at least two receptacles interconnected by a connection line, care is taken to perform the cutting so as to preserve the connection line, in which case only the covering strip is cut through on the path corresponding to the connection line. The cutting tool comprises a blade which co-operates with an anvil blade in order to cut simultaneously through both strips over their entire thickness outside the connection lines, and in the connection lines to cut through only the covering strip while merely biting into only a fraction of the thickness of the strip of thermoplastic material. The cutting tool and the backing tool then need to be positioned with accuracy of 5 micrometers (xcexcm) in the plane of the strip of thermoplastic material.
When the receptacles are re-entrant, with the diameter of the rim of each receptacle being smaller than the diameter of the body of the receptacle, the lower backing tool must be made in the form of at least two separable elements that need to be moved both vertically and radially towards the axis of the receptacle prior to performing cutting proper by lowering the cutting tool. That disposition requires complex moving parts and it is difficult to obtain the required accuracy of 5 xcexcm. It also requires sufficient clearance to be left between the bodies of the receptacles to leave room to pass the separable elements of the backing tool, as they move up and down.
A difficulty of the same kind arises in the station for thermoforming re-entrant receptacles. Thermoforming molds are made as two separable portions. Nevertheless, when the molds are assembled together there are no obstacles, and the problem of separation occurs only for unmolding. In addition, the shape of the molding pistons does not require the molds and the pistons to be positioned relative to one another during thermoforming with precision of 5 xcexcm.
An object of the invention is to provide a method and an installation of the kinds mentioned in the introduction, making it possible simply and at low cost to separate filled and closed receptacles from the strip of thermoplastic material.
In the method of the invention, this object is achieved by the fact that prior to thermoforming a row of receptacles, preliminary cuts separated by attachment points are formed in a transverse stripe of the strip of thermoplastic material used for thermoforming a row of receptacles in a subsequent cycle, said preliminary cuts defining practically the entire final periphery of the rim of each receptacle that is to be thermoformed, the attachment points being broken when the receptacles are separated in a subsequent cycle after the filled receptacles have been closed.
Thus, a large fraction of the cutting of the periphery of each receptacle is implemented on a plane portion of the strip of thermoplastic material.
Advantageously, the attachment points are broken by pressing moving pistons against the rims of the receptacles, said pistons co-operating in particular with stationary backing tools placed between the receptacles in a row.
In order to ensure that the strip of thermoplastic material is sterile, the preliminary cuts are made by melting the material of the thermoplastic strip.
In order to limit losses of plastics material between two transverse rows of receptacles, prior to thermoforming, a scrap zone of the strip of thermoplastic material extending between two consecutive transverse stripes is subjected to stretching.
Most advantageously, prior to closing the filled receptacles, a row of coverings are cut out in a covering strip that advances stepwise. The coverings are cut out around an outline adapted at least in part to the final outline of the rims of the receptacles. Each covering can present a pull tab located on the outside beyond a discontinuous line of cut in the corresponding filled receptacle. During a treatment cycle, a row of coverings are cut out, they are brought over a row of filled receptacles, they are steadied on the rims of the receptacles by spot connections, and they are sealed to the rims of the receptacles in a subsequent cycle.
To reduce wastage from the covering strip, a row of coverings cut out from a covering strip of width that is smaller than the width of the strip of thermoplastic material. Preferably, the size of the advance step of the covering strip is smaller than the size of the advance step of the thermoplastic material.
The installation of the invention includes, upstream from the thermoforming station, a preliminary cutting station suitable for making preliminary cuts separated by attachment points in a transverse stripe of said strip of thermoplastic material used for thermoforming a row of receptacles in a subsequent cycle, the preliminary cuts defining practically the entire final periphery of the rim of each receptacle that is to be thermoformed, and the separator station has means for breaking said attachment points in a subsequent cycle.
Preferably, the means for breaking the attachment points of a row of filled and closed receptacles comprise vertically movable pistons bearing against the rims of said receptacles and cooperating in particular with stationary backing tools placed between the receptacles of said row.
Advantageously, the preliminary cutting station has tools for hot cutting.
The installation further comprises, upstream from the thermoforming station, stretching means for stretching a scrap zone of the strip of thermoplastic material, the scrap zone extending between two consecutive transverse stripes.
It also comprises means for advancing a covering strip stepwise, means for cutting out a row of coverings, means for bringing them over a row of filled receptacles, means for causing the covering to be held in position on the rims of the corresponding receptacles during one cycle, and means for sealing the covering on the rims during a subsequent cycle.